A New Dynamic Climate-Based Daylight Metric for Sustainable Building Design in Hot Climates

Muhammad Adel A. Mahmoud1, Islam Ayman Mashaly2, Yussra Mohamed Rashed2, and Khaled Nassar2

1. Housing and Building National Research Center (HBNRC), Egypt

2. Department of Construction and Architectural Engineering, American University in Cairo, Egypt

Abstract: Daylight performance metrics are moving away from the traditional daylight factor and average illuminance to more climatic-based metrics such as Daylight Autonomy (DA) and Useful Daylight Index (UDI). These metrics offer a better measure of the daylight performance throughout the year and incorporate the varying weather conditions and as such are dubbed climatic-based metrics. However, in hot climates where the ratio of direct to diffuse is highest, achieving these metrics may result in over-heating the spaces. Achieving acceptable climatic-based metrics for the space may result in unacceptable heat gains. The Day light Autonomy and the Useful Daylight Index do not account for the total amount of lux-hours achieved throughout the year. The solution thus far has been to run coupled-energy and daylight simulations and in order to assess the effect of achieving certain climatic-based metrics on the heat gain and thermal performance of the space. In this paper a new metric is proposed that takes into account the total amount of lux-hours achieved throughout the year and the irradiation for different time step into a single measure. Details about the measure and sample test cases are presented.

Key words: climate-based, simulation, daylight, sustainability